1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light [herein used in a broad sense, including untraviolet rays, visible light, infrared rays, X-rays, gamma-rays, and the like].
2. Description of the Prior Art
Photoconductive materials constituting photoconductive layers in solid state image pick-up devices or in the field of image formation, for electrophotographic image-forming members or manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as safety to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid safety characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as a-Si]has recently attracted attention as a photoconductive material. For example, DE-OS Nos. 2746967 and 2855718 disclose its applications for use in image forming members for electrophotography, and DE-OS No. 2933411 its application for use in a photoelectric converting reading device.
However, under the present situation, photoconductive members having photoconductive layers of a-Si of the prior art are further required to be improved in overall characteristics, including electrical, optical, and photoconductive characteristics such as dark resistance value, photosensitivity, and responsiveness to light, and use environment characteristic such as humidity resistance, and further in stability with lapse of time.
For example, when a-Si is applied to an image forming member for electrophotography, if it is attempted to obtain higher photosensitivity and higher dark resistance, there may occur generation of residual image due to residual potential during repeated uses over a long time, namely the so-called ghost phenomenon. Further, since the surface of the photoconductive layer is subjected continually to chemically and physically severe conditions such as corona charging, friction with toner and paper or cleaning with blade, whereby vital image defects may sometimes be formed as the change with lapse of time.
Further, when a photoconductive layer is made of a-Si material, in order to improve its electrical and photoconductive characteristics, hydrogen atoms or halogen atoms such as fluorine atoms or chlorine atoms, and in order to control the conductivity type, boron atoms or phosphorus atoms, or in order to improve other characteristics, other atoms are incorporated as the constituent atoms in the photoconductive layer. However, depending on the mode in which these constituent atoms are contained, there may sometimes occur problems in electrical and photoconductive characteristics.
In particular, in the layer region at the outermost surface of the photoconductive layer, dangling bonds are liable to be formed during manufacturing process depending on the content of the contained atoms and their distribution. For this reason, the problems of behavior of charges variously changed and structural stability are very important. It is frequently determined by the number of dangling bonds in the layer region at the outermost surface of the photoconductive layer whether the photoconductive member can exhibit the function as desired.
On the other hand, when a photoconductive member is prepared as an image forming member for electrophotography according to the method conventionally known in the art, there have been various problems. For example, due to insufficient life of photocarriers generated by irradiation of light in the photoconductive layer formed within said layer, sufficient image density could not be obtained, or in the case of greater dosage of image exposure, excessive photocarriers formed in the vicinity of the surface of the photoconductive member may be propelled in the lateral direction. Further, injection of charges from the support side could not sufficiently be impeded, whereby the images tended to be unclear.
Therefore, when a photoconductive member is made of an a-Si material, it is necessary to provide a photoconductive layer having the electrical and optical characteristics as mentioned above and a chemically and physically stable surface protective layer while maintaining these characteristics, and high quality images can be obtained for a long time with such a layer structure.